The present invention generally relates to charged particle beam exposure methods and apparatuses, and more particularly to a charged particle beam exposure method which is used for producing large scale integrated circuits (LSIs) and an apparatus which employs such a charged particle beam exposure method.
Recently, in order to further improve the integration density of integrated circuits (ICs), charged particle beam exposure methods which use an electron beam or the like are replacing the conventional photolithography technique when forming fine patterns.
FIG. 1 shows an essential part of an example of a proposed electron beam exposure apparatus. The proposed electron beam exposure apparatus includes an electron gun 1 which emits an electron beam 2, a rectangular beam shaping aperture 4, a lens 5, a deflector 6, input deflectors 8 and 9, a stencil mask 10, output mask deflectors 11 and 12, a mask deflector driving circuit 13, a lens 14, blanking electrodes 15, a reduction lens 16, a round aperture 17, projection lenses 18 and 19, deflectors 20, and a stage 22 on which a wafer 21 is placed. An optical axis is noted by a numeral 3. The lens 7 forms the electron beam 2 into a parallel electron beam, and the lens 14 converges the parallel electron beam.
In this electron beam exposure apparatus, the electron beam 2 emitted from the electron gun 1 is accelerated by an acceleration voltage which is applied across a cathode and an anode and is formed into a beam having a rectangular cross section by the rectangular beam shaping aperture 4. The shaped beam is passed through the lens 5 and the deflector 6 and is formed into the parallel electron beam by the lens 7. The parallel electron beam is deflected by the input mask deflectors 8 and 9 and passes through an aperture which is formed in the stencil mask 10. The input mask deflector 9 deflects the parallel electron beam in a direction parallel to the optical axis 3, that is, in a direction perpendicular to the stencil mask 10. The parallel electron beam is returned onto the optical axis 3 by the output mask deflector 11, and is further deflected by the output mask deflector 12. Deflector 12 matches or continues the irradiating direction of the parallel electron beam to the optical axis 3, and the parallel electron beam is thereafter converged by the lens 14. The parallel electron beam then passes through the blanking electrodes 15, the reduction lens 16, the round aperture 17, the projection lenses 18 and 19 and the deflectors 20 and is irradiated onto the wafer 21.
For example, the stencil mask 10 has a structure shown in FIG. 2. The stencil mask 10 shown in FIG. 2 includes apertures 23 through 31 which are used for forming patterns, and apertures 32 through 35 which are used for calibrating the deflection quality i.e. amount or extent of the electron beam 2. The aperture 23 is used to form the cross sectional shape of the electron beam 2 into a rectangle having an arbitrary size. The apertures 24 through 27 are used to form the cross sectional shape of the electron beam 2 into a basic shape of a repetition pattern. The apertures 28 through 31 are used to form the cross sectional shape of the electron beam 2 into a triangle having an arbitrary size.
FIG. 3 shows a part of the stencil mask 10 having the aperture 28. By deflecting the electron beam 2 as indicated by an arrow in FIG. 3, it is possible to form the cross sectional shape of the electron beam 2 into a triangle of a desired size.
When drawing a repetition pattern on the wafer 21 using the apertures 24 through 27, it is simply necessary to irradiate the electron beam 2 onto the stencil mask 10 so that the electron beam 2 irradiates one of the apertures 24 through 27 at one time. In other words, the electron beam 2 simply needs to generally irradiate a rectangular region indicated by a phantom or dashed line in FIG. 2. For this reason, the calibration of the deflection quantity of the electron beam 2 need not be extremely accurate.
On the other hand, when drawing a triangular pattern of a desired size on the wafer 21 using the apertures 28 through 31, the calibration of the deflection quantity of the electron beam 2 must be extremely accurate because the size of the triangular shape changes depending on the irradiating position of the electron beam 2 on the stencil mask 10. The calibration of the deflection quantity of the electron beam 2 is desirably carried out when forming the triangular patterns, or other variable non-rectangular patterns and the like taking into consideration the rise in temperature within the electron beam exposure apparatus after the start of the exposure, the charge-up of the apparatus and the like are considered. In other words, the apertures 24 through 31 of the stencil mask 10 for forming the non-rectangular patterns are generally located at the peripheral part of the stencil mask 10, while the aperture 23 for forming the rectangular pattern is generally located at the central part of the stencil mask 10 because rectangular patterns are used more often. However, at the peripheral part of the stencil mask 10, the position of the electron beam 2 is more likely to deviate in response to the temperature change and the charge-up since the electron beam 2 is deflected over a relatively large range.
In the conventional electron beam exposure apparatus, the calibration of the deflection quantity of the electron beam 2 is carried out using the calibration apertures 32 through 35 of the stencil mask 10. In order to ensure accuracy, such a calibration must be made quite frequently. However, there is a problem in that the calibration of the deflection quantity of the electron beam 2 using the calibration apertures 32 through 35 requires a complex and time-consuming process. As a result, the throughput of the electron beam exposure apparatus becomes poor.